System for radio spectrography



June 22, 1937. H. H. BEVERAGE 2,084,760

SYSTEM FOR RADIO SPECTROGRAPHY Filed April 10, 1934 l v HMM/wc' iGEA/194 70,9

6,4' lde INVENTOR H. H BEVERAGE I ATTORNEY FREQUENCY Patented June 22,1937 PATENT oFFlcE SYSTEM FOR RADIO SPECTROGRAPHY Harold li.Beverage,Riverhead, N. Y., .assignor to Radio Corporation of America. acorporation of Delaware Application April 10, 1934, Seriai No. 719,827

16 Claims.

In many cases it is necessary to analyze the sideband spectrum which isbeing radiated by a transmitting station. If the transmitter is beingover-modulated, the sidebands may be numerous and may extend over a widefrequency band thereby creating interference on neighboring channels.This diiiiculty occurs quite frequently in the case of transmitters usedfor telegraphic service wherein the transmitters are modulated toovercome the elects of fading.

In order to measure the radio spectrum emitted by a given transmitter,it is necessary to use a receiving device which is sharp enough toselect each sideband independently of the carrier and f Vall of theother sidebands. After a given sideband has been isolated, its intensitymay be measured in comparison with the intensity of the carrier. It isalso necessary to measure the frequency of each sideband in relation tothe carrier.

In the past, these spectrum measurements have been made manually byusing a receiver terminating in a narrow band-pass filter with a vacuumtube voltmeter associated with the output of the band-pass filter. Thefrequency and the intensity of each sideband had to be carefullymeasured, each in turn, so that this process was very long and tedious,particularly if' the transmitting station was sending only intermittenttest letters which is frequently the case.

It is the purpose of my invention to make these measurementsautomatically or semi-automatically with great speed as compared to themethods used in the prior art. Brieiiy I propose to use a cathode raytube in which the horizontal axis is made proportional to the frequencywhile the vertical axis is proportional to the intensity of theindividual sidebands and the carrier. By this method a pattern of thecarrier and the numerous sidebands is built up on the cathode ray tubeand this pattern may be photographed Vor each sideband may be measuredwith a suitable scale.

The novel features of my invention have been pointed out withparticularity in the claims appended hereto. The nature and operation ofmy invention will be better understood by the following detaileddescription thereof and therefrom when read in connection with theattached drawing in which:

Figure 1 is a circuit diagram including the essential elements forcarrying out my invention;

while,

Figure 2 illustrates the mannerin which the components of the waveanalyzed by the circuit arrangement of Figure 1 appear on a visual indi-.55 cator connected with the circuit of Figure 1,

rteferring to Figure 1, an antenna. 5 includes an inductance 6 coupledto an inductance The inductance 1 may be tuned by a variable condenser 8and the parallel tuned circuit may b e connected as shown between thecontrol grid and 5 cathode of a thermionic tube Il which serves toamplify any radio frequency energy picked up by the antenna. The anodeelectrode of tube I4 may be coupled by way of a choking inductance i5and coupling condenser I6 to the control grid 10 of a thermionicdetector 2|'. The input circuit of the detector 2| may include aninductance l'| tuned by a variable capacity I8, the parallel circuitbeing coupled as shown between the control grid and cathode of tube 2|.An oscillation gen- 15 erator comprising a tube 26 having its controlgrid and anode connected to its cathode by way of coupled circuitsincluding an anode inductance 25 and an inductance 23 and tuningcapacity 24 connected as shown between the control grid and 20 cathodeof tube 26 may be used to produce sustained oscillations of the desiredfrequency. The oscillations produced in 26 and its circuits may beimpressed on an additional electrode 22 in the detector by means of alead connected as shown 25 to a movable point on the inductance 23.

The anode electrode of tube 2| is connected as shown to an inductance 29which may be tuned to the desired intermediate frequency by a capacity30. The inductance 29 is coupled as shown to an inductance 32 connectedwith an intermediate frequency amplifier 33. The intermediate frequencyamplifier 33 is connected with an inductance 34 which impressesamplified intermediate frequency energy on an inductance 35 35 connectedwith the input electrodes of a full wave rectifier 3S. The intermediatefrequency amplier should include tuned filter circuits and should beextremely selective. Preferably the intermediate frequency amplifier 33includes a crystal 40 filter of the type disclosed in Hansel] UnitedStates application No. 564,770, filed Sept. 24, 1931, Patent #2,001,387,dated May 14, 1935. The rectied current in the output of the full waverectifier 36 passes through a load resistor 31. The 45 thermionic tube39 has its control grid and cathode connected as shown by way of asource 38 across a variable portion of 31. 'I'he source 38 supplies asuitable bias to the control grid of 39. This bias may be adjusted sothat when no energy 50 is being received from the intermediate frequencyamplier, tube 39 is cut off and there is no voltage drop throughresistance 40 connected between the anode and cathode of 39. On theother hand, when energy is received from the intermediate frequencyamplifier. a positive potential drop is developed across resistance 31and tube 39 draws anode current from battery 4I through resistance 49 inproportion to the energy received from the intermediate frequencyamplifier. This relation is substantially linear if the resistance 31 ismade high enough as compared to the impedance of the rectifier 38. Thevoltage drop across the resistance 40 is applied as shown by leads tothe control or deflecting plates 42 and 43 of a cathode ray tube. Thecathode ray tube may include an electron stream producing electrodeenergized as shown. The cathode ray beam is deflected from its normalpath vertically, an amount propor-I tional to the voltage supplied tothe control plates 42 and 43. If the rectifier system and the couplingtube 39 and resistance 40 are made linear by the method disclosed above,the deflection of the stream will be proportional to the intensity ofthe carrier or particular sideband producing the intermediate frequencyenergy which passes through the intermediate frequency amplifier.Obviously, if the receiver is tuned through the frequency spectrum ofthe wave to be energized, the vertical deflection of the electron streamin the cathode ray tube will indicate the relative intensities of theseveral sidebands and the carrier as they are passed through, and if thecathode ray beam is also moved horizontally in proportion to the amountof frequency shift produced in the tuning of the receiver, each sidebandwill be spread out in its proper place in relation to the carrier bothas to frequency spacing and as to amplitude.

In my invention I create this spread by automatically shifting thestream horizontally, an amount proportional to the change in frequencyas the receiver is tuned. To do this, a motor I3 drives a shaft I2 whichin turn drives three small variable condensers comprising rotor plates48. 2li and I0. In addition to this, these rotor plates cooperate withcorresponding stator plates 41, I9 and 9 to tune the oscillator, thedetector and the radio frequency amplifier respectively. In addition,the shaft I2 also drives a contact point I on a potentiometer 4. Thecontact point I is insulated from ground by insulating bushing Il.Condenser plates 9 and III tune the input to the radio frequencyamplifier, plates I9 and 20 change the tuning of the detector andcondenser plates 41 and 48 change the frequency of the oscillator. Thesecondensers .are so proportioned that the oscillator and the tunedcircuits of the receiver are kept in step to produce an intermediatefrequency wave of the desired frequency. The

range which may be covered by these small con-- densers may beadjustedby varying the value of the padding condensers 53 which are connected inseries with the variable condensers as shown. l

From the above it will be obvious that the position of the contact arm Iwill be synchronous with the position of the rotors I0, 20 and 48 of thevariable condensers since all of these devices are driven by shaft I2.Consequently, the varying voltages drawn-from source 2 connected withthe potentiometer 4 will be applied by way of line L to plate 45 of thecathode ray tube, plate 44 of which is grounded, and will move theelectron stream horizontally in proportion to the change of frequency inthe receiver. The path followed by the stream may be made visible in anymanner. For example, the cathode ray tube may include\a screen or targeton whichA the beam falls and adjustments may .be .made such that thecarrier C will appear in the center of the screen or target, while thepairs of sidebands a--a', b--b, d-d', e-e' will appear as shown at 5I ofFigure 2, which represents the screen of the cathode ray tube. Thescreen of the cathode ray tube may be photographed or the intensity ofeach sideband may be measured with a scale 52 on or adjacent to thescreen, or a piece of thin paper may be placed over the cathode rayscreen and the sideband intensities may be drawn upon the paper sincethe pattern may be seen through the paper. In cases where it is possibleto operate the motor I3 at several revolutions per, second, a fixedpattern may be made to appear on the cathode ray screen.A However. inmany cases this may involve some difficulties and it will be necessaryto operate the motor at a lower speed such as one to two revolutions persecond. In this case the sidebands are created on the screen one afterthe other very rapidly and if fluorescent material is used so that thelight will persist for a second or more, a complete pattern maybe seeneven though the motor I3 is turning quite slowly. The horizontal scaleon the cathode ray screen may be readily calibrated in terms offrequency by introducing a pair of known frequencies on the screen froma source of known frequency. A convenient method for doing this is shownin Figure l wherein 54 is a piezo-electric oscillator coupled through asuitable harmonic generator 55 to an inductance 56, which may in turn becoupled to the input of the receiver. By impressing waves of frequencywhich are known on the rectifier and on the cathode ray tube thehorizontal scale may be calibrated. A similar method of calibration hasbeen described by Mr. Braaten and Mr. Peterson in an I. R. E. paperentitled The Precision Frequency Measuring System of R. C. A.Communications, Inc. in June 1932.

While I have shown a preferred form of my invention, it is obvious thatthere are several possible modifications without departing from thescope of my invention. For example, while I have shown only one stage ofradio frequency amplification in tube I4, I could use as many stages asmight be deemed necessary by merely adding more condensers which may bedriven by shaft I2. It is also obvious that if the range to be coveredis not so much as to extend beyond the limits where the selectivity ofthe high frequency circuits becomes appreciable, it will be unnecessaryto vary the tuning of the high frequency circuits and only theoscillator condenser 41-48 and the potentiometer arm I will have to bedriven by the motor I3. While I have shown the rectifier 3B associatedwith tube 39, it is obvious that I could apply the output of theintermediate frequency amplifier 33 directly to the cathode ray controlplates 42 and 43, in which case the pattern on the cathode ray screenwould be the same as that shown excepting that it would extend equallyabove and below the center line. Also, while I mention that a crystalfilter is preferable for obtaining thevery sharp selectivity in theintermediate frequency amplifier 33,

it would also be possible to beat the frequency down to audio frequencyinstead of intermediate frequency, enabling one to use a narrow audiofrequency band-pass filter.

Having thus described my invention and the operation thereof, what Iclaini'is:

1. 'I'he method of analyzing energy including the carrier and sets ofupper and lower side bands, resulting from the modulation of a carrierwave sidebands and said side `bands and carrier and producingindications characteristic of the amplitude of said impulses and of thetime intervals therebetween. l

2. The method of analyzing the energy including the carrier and sets ofupper and lower sideband waves, resulting from the modulation of acarrier by a modulating potential to produce modulation which includesthe steps of, producing direct current impulses the amplitude of whichare characteristic oi' the amplitude of the said carrier/and varioussidebands, producing visual indications of the amplitude of saidimpulses, and separating said visual indications as to time by intervalscharacteristic of the frequency spacing between` said sidebands and saidsidebands and carrier.

3. The method of analyzing the carrier energy and sideband energyresulting from the modulation of a carrier by a modulating potentialwhich includes the vsteps of, producing directl current impulses, theamplitude of which are characteristie of the amplitude of the saidcarrier and various sidebands, producing potential variationscharacteristic of the amplitude of said impulses, producing an electronstream, applying said potential variations to said electron stream toiniiuence the path thereof to thereby produce visual indications, andsimultaneously influencing the path of said electron stream to separatesaid visual indications by time intervals characteristic of thefrequency differences between said carrier and sidebands.

y4. The method of analyzing energy including the carrier and sets ofupper and lower sidebands, resulting from the modulation of a carrierwave by modulating potentials which includes the steps of, producingimpulses the amplitude -of which are proportional. to the intensity ofthe said carrier and various sidebands respectively, separating saidimpulses as to timeby intervals proportional to the frequency spacingbetween said sidebands and said sidebands and carrier, and producingvisual indications of said impulses which are characteristic of theamplitude thereof and of the spacing thereof.

5. The method of analyzing the energy including the carrier and sets ofupper and lower sideband waves, resulting from the modulation of acarrier by a modulating potential4 to produce modulation which includesthe steps of, producing impulses the amplitude of which are proportionalto the intensity of the said carrier and various sidebands respectively,producing visual 4indications of the amplitude of said impulses, and

separating said visual indications as to time by intervalscharacteristic of the frequency spacing between said sidebands and saidsidebands and carrier.-

6. The method of analyzing the carrier energy and sideband energyresulting from the modulation of a carrier by a modulating potentialwhich includes the steps of, producing impulses the amplitude of whichare characteristic of the amplitude of the said carrier and varioussidebands, producing potential variations characteristicof the amplitudeof said impulses, producing an electron stream, applying said potentialsto said electron stream to influence the path thereof to thereby producevisual indications, producing other potentials which are al function ofthe frequency difference between said carrier andlsaid sidebands, andapplying said other potentials to said electron stream to influence thepath thereof.

7. A monitoring .device to be used to analyze the character of energyresultingfrom the modulation of a carrier wave by modulating potentialscomprising in combination, a` receiver, a cathode ray tube havinganelectron stream producing -:device and sets of deflecting platesadjacent said stream, a connection between the output of said receiverand one set of said deiiecting plates, means for tuning said receiverthrough a frequency range equal to the frequency band covered by saidcarrier andthe main sidebands produced by said modulation, and means forsimultaneously applying a potential diierence between another set ofsaid plates which varies between predetermined limits as the tune ofsaid receiver .is varied through said frequency range.

S. A monitoring device to be used to analyze the character of energyresulting from the modulation of a carrier by modulating potentialscomprising in combination, a receiver, a cathode ray tube having anelectron stream producing device, a target and sets of deflecting platesadjacent said stream, a connection between the output of said receiverand one set of said delecting plates, means for tuning said receiverthrough a frequency range equal to the frequency band covered by saidcarrier and the main sidebands produced by said modulation whereby thepath of said stream is iniiucnced by the amplitude changes in the energyresulting from said modulation, and means for simultaneously applying apotential difference between another set of said plates which variesbetween predetermined limits as the tune of said receiver is variedthrough said frequency range to also influence the path r of saidstream.

9. A monitoring device to be used to analyze the character of energyresulting from the modulation of a carrier by modulating frequencycomprising in combinatioma receiver, a cathode ray tube having anelectron stream producing device, a target, a set of deecting plates forhorizontally deiiecting said stream and a set of deiiecting plates forvertically deecting said stream, a

connection between the output of said receiver :T

and said rst set of defiecting plates, means for tuning said receiverthrough a frequency range equal to the frequency band covered by saidcarrier and the main sidebands produced by said modulation, and meansfor simultaneously applydemodulator, a rectifier connected to saidinterwith another pair of said plates, and means for varying thepotential of said source and the tune of said oscillator simultaneously.

1l. A radio receiver including a tuned radio frequency amplifier, alocal oscillator including tuning means and a demodulator connected tosaid tuned amplifier and said local oscillator, an intermediatefrequency amplifier connected to said demodulator, a rectifier connectedto said intermediate frequency amplifier, a cathode ray tube having anelectron stream producing system and sets of deecting plates adjacentthe normal path of said stream, a coupling between the output of saidrectifier and a pair of said plates, 'a variable source of directcurrent connected 'with another pair of said plates, and means forvarying the potential of said source of direct current and the tune ofsaid oscillator and the tune of said amplifier simultaneously.

12. A radio receiver including a tuned radio frequency amplifier, atuned local oscillator and a demodulator connected to said amplifier andsaid local oscillator, an intermediate frequency amplifier connected tosaid demodulator, a full wave rectifier connected to said intermediatefrequency amplifier, a cathode ray tube having an electron streamproducing systeml and a first pair of defiecting plates mounted on anaxis passing through the normal path of said stream, and a second pairof defiecting plates mounted on an axis passing through the normal pathof said stream at an angle with respect to said first named axis, acoupling between the output of said rectifier and said first pair ofsaid plates,

a -variable source of direct current connected4 with said second pair ofsaid plates, and means for continuously varying the potential of saidsource and the tune of said oscillator simultaneously. 13. In amonitoring device to be used to analyze the character of wave energyresulting from the modulation of a carrier wave by modulatingootentials, wave amplifying means and demodulating means which whenenergized has an output the amplitude of which is characteristic of anarrow band of frequencies impressed on the input, means for impressingsaid wave energy on said amplifying means, a cathode ray tube having anelectron stream producing device and sets of defiecting plates adjacentsaid stream, a connection between the output of said demodulating meansand one set of said defiecting plates, means for tuning said amplifyingmeans through a frequency range equal to the frequency band covered bythe carrier and the main side bands of said wave energy produced bymodulation, and means for simultaneously applying a potential differencebetween another set of said plates which varies between predeterminedlimits as the tune of said amplifying means is varied through saidfrequency range.

14. In a radio receiver, modulated wave in- I tercepting and amplifyingmeans which is tunable, a tunable local oscillator, a demodulatorconnected to said amplifying means and to said local oscillator, asharply tuned intermediate frequency amplifier connected to saiddemodulator, a cathode ray tube having an electron stream producingsystem and sets ofrdefiecting plates adjacent the normal path of saidstream, a coupling between the output of said intermediate frequencyamplifier and a pair of said plates, a. variable source of directcurrent connected with another pair of said plates, and means forvarying the potential ofvsaid source and the tune of said amplifyingmeans and oscillator simultaneously.

15. The method of analyzing energy comprising a. carrier 4wave and theside band frequencies which result from modulating said carrier wave inaccordance with signals which include the steps of, successivelyresonating energy characteristic of the various frequencies in thefrequency spectrum; covered by said carrier and side bands, producingimpulses the amplitude of which are characteristic of the intensity ofthe resonated energy, synchronously producing potentials the amplitudeof which are characteristic of spacing of the frequencies of saidspectrum covered by said carrier and side band, producing an electronstream the path of which is controllable, controlling the path of saidstream in accordance with the amplitude of said potentialscharacteristic of the intensity of said resonated energy and controllingthe path of said stream in accordance with said synchronously producedpotentials.

16. A radio receiver including a tunable radio frequency amplifier, atunable local oscillator, a demodulator connected to said amplifier andto said local oscillator, an intermediate frequency amplifier connectedto said demodulator, a full wave rectifier connected to saidintermediate frequency amplifier, a cathode ray tube having an electronstream producing system and a first pair of deflecting plates mounted onan axis passing through the normal path of said stream, and a secondlpair of defiecting plates mounted on an axis passing through the normalpath of said stream at an angle with respect to said first named axis, acoupling tube having a control grid normally ,biased to cut off saidtube having an output electrode, a coupling between the output of saidrectifier and said control grid, a coupling between said outputelectrode and said first pair of said defiecting plates, a variablesource of direct current connected with said second pair of defiectingplates, and means for continuously varying the potential of said sourceof direct current and the tune of said radio frequency amplifier andsaid oscillator simultaneously.

HAROLD H. BEVERAGE,

